1. Field of the Invention
The present invention relates to an apparatus for controlling an internal pressure of a hermetically sealed chamber to maintain the internal pressure at a prescribed pressure level.
2. Description of the Related Art
There have widely been used apparatus with a hermetically sealed chamber, such as an aseptic filling machine for filling a container in an aseptic environment with a processor such as a filling machine or the like in an isolator (see Japanese laid-open patent publication No. 2002-301138). Specifically, Japanese laid-open patent publication No. 2002-301138 discloses an isolator system including an isolator serving as an isolating device which houses therein a production facility such as a powder filling machine and a sterilization casing serving as a pass box for sterilizing an object such as a raw material to be delivered to the powder filling machine and then carrying the sterilized object into the isolator.
The isolator has a hermetically sealable structure for fully blocking a direct influx of ambient air to provide therein a hermetically sealed environment, i.e., a hermetically sealed chamber, that is fully isolated from the external environment. After the isolator is decontaminated with a decontaminating gas such as a hydrogen peroxide vapor or the like introduced therein, the isolator regulates a rate at which air is sent thereinto through an inlet port equipped with an aseptic filter such as a HEPA filter and a rate at which air is discharged therefrom through an outlet port equipped with an aseptic filter such as a HEPA filter, thereby keeping a prescribed positive pressure in the isolator. While the isolator is in operation, therefore, it keeps an aseptic environment therein by preventing ambient air from directly flowing thereinto instead of through the aseptic filters. The sterilization casing also has a hermetically sealable structure for accommodating an object therein. After an object placed in the sterilization casing is decontaminated by a decontaminating gas supplied to the sterilization casing, a joint between the sterilization casing and the isolator is opened and the object is delivered from the sterilization casing into the isolator. It is desirable to keep a prescribed positive pressure in the sterilization casing in the same manner as with the isolator. In recent years, it has been customary to keep a prescribed positive pressure in the sterilization casing by regulating a rate at which air is sent thereinto and a rate at which air is discharged therefrom.
If the internal pressure of the isolator and the sterilization casing is kept at an excessively high pressure level, then they need to have a hermetically sealed structure strong enough to withstand the high pressure. Therefore, it is the usual practice to keep a positive pressure slightly higher than the atmospheric pressure of the external environment, in the isolator and the sterilization casing.
After an object is placed in the sterilization casing, i.e., a hermetically sealed chamber, the sterilization casing is supplied with a hydrogen peroxide vapor to decontaminate the object. At this time, the internal pressure of the sterilization casing may quickly rise beyond the upper limit of an allowable positive pressure range for the sterilization casing. If the internal pressure of the sterilization casing is about to increase beyond the upper limit of the allowable positive pressure range, then a discharge valve connected to the sterilization casing is opened to lower the internal pressure. However, since the gas in the sterilization casing is discharged therefrom at this time, the introduced hydrogen peroxide vapor is also discharged, failing to decontaminate the object. Another problem is that if the introduced hydrogen peroxide vapor causes an abrupt internal pressure buildup in the sterilization casing, then the internal pressure of the sterilization casing may become uncontrollable. These problems manifest themselves particularly with containers having relatively small volumes, such as sterilization casings (decontamination casings) and pass boxes.
When the hydrogen peroxide vapor introduced into the hermetically sealed chamber is subsequently condensed in the decontamination process, the internal pressure of the hermetically sealed chamber may sharply drop below the lower limit of the allowable positive pressure range. If the internal pressure of the hermetically sealed chamber is going to drop below the lower limit of the allowable positive pressure range, then air is introduced into the hermetically sealed chamber to increase the internal pressure into the allowable positive pressure range. However, the introduced air reduces the density of the hydrogen peroxide vapor in the hermetically sealed chamber, so that the hydrogen peroxide vapor tends to fail to decontaminate the object. In the event that an abrupt internal pressure drop occurs in the hermetically sealed chamber, the internal pressure of the sterilization casing may become uncontrollable. These problems manifest themselves particularly with containers having relatively small volumes, such as sterilization casings (decontamination casings) and pass boxes.